The maintenance of well-functioning mitochondria plays a key role in neuronal health. In the previous project period, we found that neuronal injury in several neurotoxin and genetic models of parkinsonian neurodegeneration converged on eliciting increased mitochondrial turnover by autophagy (mitophagy). While mitophagy in some models is neuroprotective, in other models, inhibiting autophagy reduces neurite retraction and cell death. We hypothesize that the capacity to replace damaged/degraded mitochondria through mitochondrial biogenesis is important in determining survival-death outcomes in this context. Preliminary data indicate a key role for extracellular signal-regulated protein kinase 2 (ERK2), which shows an altered mitochondrial distribution in Parkinson's disease midbrain neurons, in regulating both mitophagy and mitochondrial biogenesis. We will utilize differentiated neuroblastoma cells, primary embryonic mouse neurons and in vivo mouse models to study the mechanism(s) leading to the observed decreases in mitochondrial content and function, study the role of phosphorylation in regulating biogenesis, and determine the neuroprotective potential for strategies to modulate mitochondrial content in toxin and dominant genetic models of Parkinson's disease.